The present invention relates generally to information signal recording mediums of the electrostatic capacitance type on which an information signal is recorded as variation of geometrical shape and from which the signal thus recorded is reproduced by the variation in capacitance between the recording medium and an electrode of a tracing reproducing stylus. More particularly, the invention relates to an information signal recording medium of the electrostatic capacitance type in which the base structure thereof is formed from an electroconductive synthetic resin containing electroconductive substance.
An information signal recording medium of electrostatic capacitance type known heretofore is fabricated in the following manner. A synthetic resin is press molded by a stamper thereby to obtain a recording medium base structure on the surface of which variation of geometrical shape comprising a plurality of pits conforming to an information signal is formed. Next, a thin film of an electroconductive metal of a thickness of, for example, a number of hundreds of .ANG.ngstroms (.ANG.) is formed by evaporation deposition on the surface of this recording medium base structure. Then, on this electroconductive metal thin film, a thin film of a dielectric material of a thickness of, for example, of a number of hundreds .ANG. is applied and formed by the glow-discharge method.
As a reproducing stylus having an electrode traces over the surface of a recording medium fabricated in this manner, the electrostatic capacitance between the electrode of the reproducing stylus and the metal thin film of the recording medium through the dielectric thin film or through the dielectric thin film and an air gap varies in response to the variation of the geometrical shape of the recording medium. The recorded signal is produced by a known method in response to this variation of the electrostatic capacitance.
In the fabrication of this known recording medium, however, process steps such as the step of evaporation deposition of an electroconductive metal thin film and the step of depositing a dielectric thin plate as described above are required in addition to the step of press molding the recording medium base structure. For this reason, a considerable quantity of production equipment and many complicated and troublesome process steps are required, whereby the production cost is high.